Transmitting system



-April 5, .1938. Y F. H. KROGER' TRANSMITTING SYSTEM FiledJan. 24, 1955ATTORNEY Patented Apr. 5, 1938 UNITED STATES TRANSMIT'EING SYSTEM Fredlli. Kroger, Rocky Point, N. Y., assigner tc Radio Corporation ofAmerica, a corporation of Delaware Application January 24, 1935, SeriaiNo. 3,259

ld Claims.

This invention relates to an improved short wave transmitting system.

An object of the present invention is to provide a very simple andhighly efficient short wave f, transmitting system.

Another object is to provide a system which enables the transmission ofmodulated short wave signals over a very wide frequency band and with asubstantially flat overall characteristic.

A further object is to provide a transmitter arrangement which has highfrequency stability comparable with crystal control, but which dispenseswith the use oi" piezo-electric crystals.

A still further object is to provide an eicient short wave systemcapable of radiating waves of the order of three meters, more or less,and of providing an output which when unmodulated is between 80 and 100watts.

And a still further object is to provide a highly o advantageousassembly of elements which are inherently rugged and free from criticaladjustments and the like.

A feature of the invention lies in the combination of single endedmaster oscillator and frequency control line, which requires noinsulation in the mechanics of the line. The oscillator is thus in thesimplest possible mechanical form and, with the provision of a simplecircuit, reduces initial cost of equipment and maintenance to a minimum.

Another feature lies in the manner of mounting the equipment into acompact assembly which enables easy adjustment and maintenance ofapparatus. The entire radio frequency assembly is mounted as an integralunit whereby there can be no geometrical change.

A further feature resides in the use of lecher wires for inductivecoupling instead of lumped inductances, in order to obtain simplicity oftuning and higher operating efciency in the system. These lecher wiresare used with trimming condensers so that with change in temperaturethere will be a minimum change of electrical constants.

One advantage of the invention is that the frequency is maintainedconstant as long as the oscillator is supplied with power which hasreasonably constant voltage, that is, in a range plus or minus onepercent, and without the use of 50 numerous accessories which requireadjustment and maintenance.

Other objects, features and advantages will appear in the subsequentdetailed description taken in conjunction with the accompanying drawingwhich shows, diagrammatically, a com- (Cl. Z50-17) plete transmittingsystem in accordance with thev Line l is a low loss concentric tubeaffair havingl inner and outer conductors, and has the effect of asharply tuned resonant circuit whose reactance changes rapidly withfrequency, and it is this characteristic which is utilized to keep thefrequency of oscillator MO constant.` Since the resonant frequency ofthe concentric line is determined chiefly by its length, it is providedwith a sylphon bellows and invar rod, or equivalent arrangement S formaintaining the overall length of the inner conductor constant despiteambient temperature fluctuations.

Line l is designed to be a quarter wave length long, electrically, forreasons of reliability and simplicity. The diameters of outer and innerconcentric tubes are chosen to give a compromise between space economyand a high reciprocal of power factor; the outer tube serving as asupport for the panels upon which are mounted substantially all theradio frequency units. For greater frequency stability, line l is madeintegral with the radio frequency units and kept free from vibrationwhich is ltered out. In practice, the line and transmitter unit aresuspended by very exible helical springs, and the entire unit secured toa rack which, in turn, is mounted on shock absorbers. For a moredetailed description of line I as employed herein, reference is made tomy 'copending application Serial No. 1489, filed January 12, 1935.

As an illustration of the frequency stability of the line, in using thetwelfth harmonic of a crystal controlled oscillator for comparison, itwas found that with a variation of 9 C. in ambient temperature, line lvaried no more than the crystal which maintained Aits frequency within.0005% over this change in ambient temperature.

Line l is made single ended and the frequency produced by oscillator MOis doubled in the subsequent stage. Any other arrangement would,Ordinarily, give too long a line. In order to reifi v tion to eachother.

duce possible undesirable reaction, the generated frequency is taken asone-half that radiated, which in one practical embodiment was 45.9megacycles.

A thermo-galvanometer M is loosely coupled to the inner tube of line Iby means of exposure plates for determining the amplitude ofoscillations of the line.

Between grid 3 of vacuum tube MO and line there is provided theconventional grid leak GL which gives part of the bias for the grid,thus enabling automatic adjustment for variation in tubes.

The filament power leads for the legs of cathode K which are aboveground potential and which are maintained at the same radio frequencypotential by by-pass condenser 4, are part of a double coil 5 forcontrolling regeneration of oscillator MO. The double coil 5 serves tobring out the filament leads in known inductive rela- Condenser 1 is aVernier for varying the inductance of coil 5, and condenser 6 is aby-pass condenser to ground. A spark discharge gap |00 serves as aprotective circuit in case of breakdown of tube MO. The filament circuittuning is arranged to give suiicient regeneration at the frequency ofline but to cause 0scillations in MO to cease when line is shortcircuited.

A 220 volt, 60 cycle, alternating current som-ce energizes the filamentof the oscillator through a transformer |06 and a copper oxide rectifier|05. The direct current obtained from rectifier |05 eliminates the small120 cycle modulation which alternating current on the filament wouldcause due to the resulting variation in bias. All other filaments aresupplied directly from the 60 cycle supply.

In the output of triode MO is a parallel tuned circuit comprising lumpedinductance 9 and variable condenser 8 coupling oscillator MO to the gridof the following frequency doubler stage. Condenser 8 is a Vernier whichprovides a convenient mechanical method of varying inductance 9, andcondenser I0 is a by-pass condenser to ground.

In one embodiment used in practice, master oscillator MO delivered aboutwatts, of which about 20 watts went to the grid of the frequency doublerstage and 60 watts to line I. The tuning of condense-r 8 varies theratio of the energy delivered by MO to the line and that delivered tothe grid of the frequency doubler. The greater this ratio, the more willbe the line current, and the less the excitation to the doubler grid,and at the same time the greater will be the frequency stability, as theline will be operating nearest to its natural frequency. A compromise isfound preferable whereby frequency stability is satisfactory and thereis sufficient grid excitation in the doubler to operate the intermediateamplifier at something less than best efficiency.

The frequency doubler stage comprises the vacuum tube FD which serves toexcite the subsequent intermediate amplifier stage with energy of doublethe frequency of that obtained from oscillator MO. Grid I3 of tube FD isconnected to the tuned input circuit comprising inductance I I andcondenser I2 tuned to the frequency of the output of oscillator MO.Inductance is not tightly coupled to inductance 9 and optimum gridcoupling is rather loose and is such as to give rather sharp tuning forgrid and plate. The output of doubler tube FD comprises variable aircondenser Il composed of two discs adjustable with respect to each otherand lecher wires I8 and is tuned to twice the frequency of the masteroscillator frequency.

A balancing air condenser 2| in the plate circuit of FD makes circuit I8symmetrical with respect to ground and is set to a value approximatelyequal to the plate-grid capacity of FD; the condenser which consists oftwo discs adjustable with respect to each other is then varied until thevoltage node of the plate circuit is approximately at its mechanicalcenter, a condition which is indicated by equal drop in wave meterindication when places equal distances on each side of the mechanicalcenter are contacted by a testing rod. Element I9 is a radio frequencyair choke coil.

Tube FD is also provided with a grid leak GL', a protective spark gapIGI, filament tuning I5 to control regeneration, variable condenser I6and condenser 58, which elements correspond respectively with elementsGL, gap |00, double coil 5, condensers 'I and 5 previously described inconnection with master oscillator MO and used for the same purposes.Other corresponding elements also appear in the subsequent power stagesin respectively corresponding locations and for similar purposes, andhence will not be referred to later.

The intermediate power amplifier stage comprises a pair of push-pullconnected vacuum tubes IPA and IP'A for amplifying the output of doublerstage FD and for exciting the grids of the succeeding power amplifiertubes. The input circuit of IPA and IPA comprises a lecher wire system28 which is bridged by a tuning air condenser 3| and which is coupled tothe lecher wires I0 in the output of frequency doubler FD. The couplingof doubler plate circuit I8 to intermediate amplifier grid circuit 28 isvaried for optimum excitation of tubes IPA and IPA'. output circuit ofthis intermediate power stage also includes a pair of lecher wires 32which are coupled through a lecher wire line |02 to the grids of thesucceeding stage. An air condenser 29 composed of two spaced discsadjustable with respect to each other aids in tuning the lecher wires32.

A pair of neutralizing air condensers 30, 34 compensate for theplate-grid capacities of the associated tubes. Element 33 is acombination of choke and parasitic resistor in the form of a coil ofresistance wire, the resistance preventing push-push parasiticoscillations. A conventional grid bias GL2 is in series with choke 33.

The power amplifier or output stage also comprises a pair of push-pullvacuum tubes PA and PA which are arranged similarly to the tubes of thepreceding intermediate amplifier stage. The purpose of this output stageis to further amplify the carrier oscillations, and it is this stagewhich is modulated and excites the antenna. The output of the poweramplifier is of the same frequency as the intermediate amplifier and iscoupled inductively to the load circuit consisting of an inductivearrangement 56 and load adjustment inductances 51, the latter eachcomprising ten turns of #10 wire, one inch in diameter and approximatelytwo inches long.

For utilization purposes, it is preferred to employ an antennacomprising a plurality of doublets of the type described in Carterapplication Serial No. 342, filed January 4, 1935.

The transmitter is capable of being either frequency modulated oramplitude modulated by connecting switch blade 53 in the plate circuitThe L Cil Sil

of the last power amplifier, either to the upper or lower contactrespectively, and by using known modulating means, not shown.

The elements of the transmitter circuit are all completely shielded andmounted on panels supported by line l.

In tuning the short wave transmitter, the iilament tuning of MO is setso that the master oscillator will not oscillate when line l is shortcircuited, after which the lament tuning is set for maximum linecurrent. In the intermediate stage, the neutralizing condensers are eachfirst set at a capacity approximately equal to the plate-grid capacityof the tubes. Then, with no plate voltage and a grid meter in circuit,the grid circuit is tuned. The plate circuit is tuned next and the dipin the grid meter noted as the tuning point is passed through. Theneutralizing condensers are each changed an equal amount and again thegrid circuit is tuned. The plate circuit is also tuned again and thegrid meter observed. If the dip in the meter is greater at the tuningpoint than previously, the neutralizing condensers should be changed inthe opposite direction. This method oi setting the neutralizingcondensers is continued until no dip is noted in the grid meter when theplate circuit is tuned, after which the grid meter is taken out of thecircuit and the plate voltage applied, and the plate circuit againtuned, the last tuning being indicated by the wave meter. The couplingof the doubler plate circuit to the intermediate amplier grid circuit isvaried or optimum exn citation of the intermediate amplifier. The nalpower amplifier stage is tuned in the same manner indicated above forthe intermediate amplifier stage.

What is claimed is:

l. In combination, an electron discharge device having anode, cathode,and grid electrodes, means for maintaining said cathode above groundradio frequency potential, a tuned input circuit connected between saidgrid and cathode electrodes, a source of radio frequency energy coupledto said input circuit, and a tuned output circuit connected between saidanode and cathode, said tuned output circuit comprising a pair of lecherwires conductively connected together at one of their adjacent ends andcapacitively coupled together at their other adjacent ends, and autilization circuit inductively coupled to said output circuit.

2. A frequency doubler comprising an electron discharge device havinganode, cathode, and grid electrodes, means for maintaining said cathodeabove ground potential, a, tuned input circuit connected between saidgrid and cathode electrodes tuned to a predetermined frequency, a sourceof radio frequency energy coupled to said input circuit, and a tunedoutput circuit connected between said anode and cathode and tuned to afrequency twice that of said input circuit, said tuned output circuitcomprising a tuning inductance in the form of a pair of parallelconductors, means for varying the tuning of said output circuit, meansfor making said pair of conductors symmetrical with respect to ground,and a utilization circuit inductively coupled to said output circuit.

3. In combination, an electron discharge device having anode, cathodeand grid electrodes, means for maintaining said cathode above groundpotential, a tuned input circuit connected between said grid and cathodeelectrodes, a source of radio frequency energy coupled to said inputcircuit, and a tuned output circuit connected between said anode andcathode, said tuned output circuit comprising a tuning inductance in theform of a pair of parallel conductors, an air condenser bridged acrossone end of said conductors for varying the inductance of said pair ofparallel conductors, and an air condenser coupling one plate of said rstair condenser to ground for making said pair oi conductors symmetricalwith respect to ground.

4. In., combination, an electron discharge device having anode, cathodeand grid electrodes, a tuned input circuit connected between said gridand cathode, a condenser connected across the legs of said cathode formaintaining both sides thereof at the same radio frequency potential, aheating source for said ilament, leads connecting the iegs oi saidcathode to said source, and a coil located between each of the legs ofsaid cathode and its associated lead for controlling regeneration, acondenser for varying the inductance of at least one of said coils, aresistance connected across said leads, and a connection from a pointintermediate the ends of said resistance to ground, a tuned outputcircuit comprising a pair of lecher wires between said anode andcathode, and a utilization circuit including another pair of lecherwires coupled to the lecher wires of said tuned output circuit.

5. A combination in accordance With claim 4, characterized in this thatsaid electron discharge device is a frequency multiplier and saidutilization circuit is a pair of push-pull connected power amplierelectron discharge devices.

6. In a sho-rt wave transmitter circuit, a pair of push-pull connectedelectron discharge devices each having anode, cathode and gridelectrodes, the corresponding electrodes of said devices being coupledtogether, a tuned input circuit connected between said grids and a tunedoutput circuit connected between said anodes', each of said tunedcircuits comprising a pair of lecher wires, a neutralizing condenserconnected between the anode of each device and the grid ofthe associatedde'- vice, means for maintaining the cathode of each device above groundpotential, a connection from a point in each tuned circuit symmetricallydis posed with respect to the lecher wires therein to the cathodes, andmeans for biasing said grids negative and said anodes positive withrespect to said cathodes.

'7. In a short wave transmitter circuit, a pair of push-pull connectedelectron `discharge devices each having anode, cathode and gridelectrodes, the corresponding electrodes of said devices being coupledtogether, a tuned input circuit connected between said grids and atunedoutput circuit connected between said anodes, each of said tunedcircuits comprising a pair of lecher wires, a neutralizing condenserconnected between the anode of each device and the grid of theassociated device, means for maintaining the cathode of each deviceabove ground potential, a connection from a point in each tuned circuitsymmetrically disposed with respect to the lecher wires therein to thecathodes, means for biasing said grids negative and said anodes positivewith respect to said cathodes, another similarly connected pair ofpush-pull coupled electron discharge devices, and a pair of lecher wiresinductively coupling the tuned output circuit of said rst push-pullcircuit with the tuned input circuit of said last push-pull circuit.

8. In a high frequency communication system, an electron dischargedevice having a high fre quency output circuit and coupled thereto acircuit tuned to an ultra high frequency, said tuned circuit comprisinga pair of lecher Wires and a variable air condenser bridging said lecherwires for tuning said circuit, said lecher wires being conductivelyshort circuited at one of their adjacent ends and bridged by said aircondenser at the other of said adjacent ends, whereby with change intemperature there is a minimum change in the electrical constants ofsaid tuned circuit.

9. In combination in an ultra high frequency circuit, an electrondischarge device having anode, cathode and grid electrodes, means formaintaining said cathode above ground radio frequency potential, a tunedinput circuit connected between said grid and cathode electrodes, asource of radio frequency energy coupled to said input circuit, and atuned output circuit comprising a pair of lecher wires conductivelyconnected together at one of their adjacent ends and capacitivelycoupled together at their other adjacent ends, a connection including aninductance coil in series with a source of potential eX- tending fromsaid cathode to those adjacent ends of said lecher wires which areconductively connected together, and a connection from said anode to theother ends of said lecher wires.

10. In combination in an `ultra high frequency circuit, an electrondischarge device having anode, cathode and grid electrodes, means formaintaining said cathode above ground radio frequency potential, a tunedinput circuit connected between said grid and cathode electrodescomprising a coil and a condenser in parallel with said coil, a sourceof radio frequency energy coupled to said input circuit, and a tunedoutput circuit comprising a pair of lecher wires conductively connectedtogether at one of their adjacent ends and capacitively coupled togetherat their other adjacent ends, a connection including an inductance coilin series with a source of potential extending from said cathode tothose adjacent ends of said lecher wires which are conductivelyconnected together, and a connection from said anode to the other endsof said lecher wires.

11. A transmitter in accordance with claim 7, including a source of highfrequency energy coupied to said tuned input circuit of said firstpushpull circuit, and means for both frequency and amplitude modulatingsaid transmitter connected to the tuned output circuit of said lastpush-pull circuit.

12. In a short wave transmitter, a single ended master oscillatorcomprising an electron discharge device having anode, cathode and gridelectrodes, a tuned input circuit comprising a quarter wave lengthconcentric frequency control line coupled between said grid and cathodeelectrodes, an output circuit for said oscillator, a frequency doublercomprising an electron discharge device also having anode, cathode andgrid electrodes, a tuned input circuit connected between said last gridand cathode and coupled to the output circuit of said oscillator, anoutput circuit tuned to twice the frequency of said oscillator coupledbetween the anode and cathode electrodes of said frequency doubler, saidlast circuit comprising a pair of lecher wires conductively coupledtogether at one of their adjacent ends and capacitively coupled togetherat their other adjacent ends, and an electron discharge device amplifierhaving an input circuit coupled to said lecher wires, said input circuitof said amplifier also comprising a pair of similarly arranged lecherWires, a utilization circuit coupled to said amplifier, an-d means formaintaining the cath- `odes of said oscillator, frequency doubler andamplifier above ground radio frequency potential.

13. A frequency multiplier comprising an electron discharge devicehaving anode', cathode and grid electrodes, means for maintaining saidcathode above ground potential, a tuned input circuit connected betweensaid grid and cathode electrodes tuned to a predetermined frequency, asource of radio frequency energy coupled to said input circuit, and atuned output circuit connected between said anode and cathode and tunedto a frequency which is a multiple of that of said input circuit, saidtuned output circuit comprising lecher wires and a variable aircondenser bridged across said lecher Wires.

14. In a high frequency communication system, a, non-oscillatingelectron discharge device having a high frequency input circuit andcoupled thereto a circuit tuned to an ultra high frequency, said tunedcircuit comprising a pair of lecher wires and a variable air condenserbridging said lecher wires for tuning said circuit, said lecher Wiresbeing conductively short circuited at one of their adjacent ends andbridged by said air condenser at the other of said adjacent ends,whereby with change in temperature there is a minimum change in theelectrical constants of said tuned circuit.

FRED H. KROGER.

